Four years after salmonella-tainted peanuts were linked to nine deaths and sparked one of the largest U.S. recalls, regulators began a health risk assessment of other nuts that have become susceptible to contamination.

The Food and Drug Administration wants to know why salmonella, which isn’t common in low-moisture foods like tree nuts, has been repeatedly linked to recalls of almonds, cashews and pistachios. Companies led by Diamond Foods Inc. and Kraft Foods Group Inc., which makes Planters, are being asked to review salmonella prevention efforts so the agency can determine how to reduce the health risk, the FDA said today in a filing.

In the past week, two closely held companies, Western Mixers Inc. and Torn & Glasser Inc., recalled pistachios because of salmonella, according to the FDA’s website. The agency didn’t single out any producers in its filing today, only referring broadly to recalls from 2009 to 2012 for pine nuts, pistachios, shelled hazelnuts, walnuts, cashews and macadamias.

“These outbreaks, published reports of salmonella in tree nuts destined for human consumption and recalls emphasize the need to assess the risk of salmonellosis associated with tree nuts intended for human consumption, and to evaluate the appropriate risk-based preventive controls,” the FDA said.

Salmonella is the most common foodborne infection in the U.S. and is commonly passed from the feces of chickens or other animals to contaminate water and produce. Contamination can lead to diarrhea, fever and abdominal cramps in humans.

Low Moisture

Low-moisture foods don’t support salmonella growth yet small amounts of the pathogen can be present in raw nuts because of the nature of the cultivation and harvesting, the Washington-based Grocery Manufacturers Association said in a 2010 industry handbook. Salmonella has emerged as a concern in the food industry after the pathogen was found in peanut butter in 2007 and 2009, the association said.

The sequence of events that led to the recent salmonella outbreaks from tree nuts isn’t fully understood, the FDA said. The agency is asking the industry, consumer groups and other experts to provide scientific data relevant to the risk assessment.

Salmonella bacteria causes salmonellosis, of which about 42,000 cases are reported each year and 400 people die from the infection, the Centers for Disease Control and Prevention, said on its website.